M., if your marriage is to survive, you really should seek counseling. Having children is very hard on a marriage. What you and your husband are experiencing is really common and with a little help, you can get your marriage back on track. Also, each of you might want to read a book called "His needs, her needs" by Willard F. Harley, Jr. It also talks about how to "affair-proof" your marriage, but the principles are the same for keeping your marriage strong and healthy under any circumstances. It really sheds light on becoming aware of each other's needs and learning how to meet them. The fact is that the separation is a two-way street. No one spouse is to blame because somewhere along the line someone's basic needs weren't met. While things can be rosy in the beginning of a marriage, when children arrive, the needs structure of your relationship as a couple gets shifted and it's hard on everyone. According to "His needs, Her needs" (and I fully believe it after 7 years of marriage and 2 small children) each of you has 5 basic needs, and they're not the same things. You may go about trying to meet his needs based on what makes YOU feel happy, and vice versa for him. The end result is that you're both spending energy on the wrong things and no one is fulfilled in the relationship.
Just to give you a glimpse of what the book covers, a man's basic needs in a marriage tend to be:
1. sexual fulfillment (no surprise here!),
2. recreational companionship (anything from playing cards to watching Monday night football, he just wants to have fun with you),
3. an attractive spouse (the meaning of this varies with each man, and the book explains it very well),
4. domestic support (the book explains this better than I can),
5. admiration (he wants you to be proud of him -- the book explains how you can work together on this because you can't be proud of him if he's not meeting your needs.)
On the other side, a woman's needs tend to be:
1. affection,
2. conversation (he does a good job of explaining to guys the type of conversation women need),
3. honesty and openness,
4. financial support (again, the book does a good job of explaining to guys how financial support meets an emotional need for women, not just a physical need), and
5. family commitment (coming home from work in time for dinner, sharing responsibilities with the kids to some extent.
One thing I've learned is that a lot of meeting each others needs has to be very intentional. It won't just happen naturally because of the distractions of work, the baby, household responsibilities, etc. And it takes both of you working at it for some successful trade-offs. If eating dinner at a certain time each day meets a "domestic support" need for my husband (this is just an example, my hubby doesn't care on this one :-)), then I have to do whatever it takes to get the food on the table at that time (leave work earlier, for example). And he might need to change something to help you meet that need, like pick the baby up from daycare. On the flip side, picking the baby up from daycare might meet some of your need for family commitment (because you're feeling stressed or rushed at work because you have to do both drop off and pick up).
Anyway, I know this is long, but I've seen lots of marriages (including my own) struggle in the early years after kids arrive. Just wanted you to know that it's common, so you're not alone, and that you (and your husband) can do something about it to not only stay married, but to have a fulfilling relationship "until death do us part" just as you (and God) intended.